1. Field of the Invention
This invention relates to packs for adhesives and/or sealants according to the preamble of the claim, to their use and to a method for filling and emptying them.
For industrial consumers, adhesives and sealants are supplied in drums or similar large-volume containers which are generally made of metal. For moisture- and/or air-curing one-component adhesives, these packs must effectively prevent the penetration of air and moisture to avoid premature curing or hardening of the adhesive/sealant. This impermeability to air and moisture has to be guaranteed during filling, transport, storage and emptying of the pack.
In view of increasingly more stringent pollution control legislation, packs of the type in question also have to be completely or at least partly recyclable. This requirement is particularly difficult to meet in the case of moisture-curing and/or air-curing adhesives/sealants because, in the case of paste-like or high-viscosity materials, the penetration of traces of atmospheric moisture, particularly during or after emptying, can lead to partial or complete hardening on the inside of the drum. This often results in coatings which adhere firmly to the inside or bottom of the drum and which make the drums difficult, if not impossible, to clean. Even where the drums are used as scrap metal, problematical combustion products can be formed from the hardened adhesive/sealant residues.
2. Discussion of Related Art
DE-C-36 05 422 describes a method of filling and emptying a container for a flowable material, the material in question being introduced into a flexible inner pack impervious to the material. This inner pack is adapted to the dimensions of the outer transport container, generally a metal drum or sealed tin container. In this method, the bag-like inner pack is first filled with the flowable material in a pot-like temporary container by means of a suitable filling unit. The dimensions of the temporary container are somewhat smaller than the corresponding inner dimensions of the actual transport container. A stiff cover plate is then placed on the surface of the material and the inner pack is tightly closed at its upper end by folding the edges over one another and welding them together. The inner pack thus filled and sealed is then turned through 180.degree. together with the temporary container and placed on the somewhat larger transport container so that the filled and sealed inner pack can be introduced into the transport container. The transport container is then closed with a lid. After transport to the point of use, the lid is taken off to remove the material, after which the material is removed by means of a suitable pump. The pump is best connected to a pressure follower plate. After an opening has been cut into the flat surface, the pressure follower plate is applied and the material to be removed is forced out upwards through compression of the inner pack. The method according to DE-C-36 05 422 is also described in detail in Adhesion 1987, No. 12, pages 25-26.
In the case of particularly sensitive materials, it is not sufficient for the inner pack to be impervious solely to the material introduced. Accordingly, DE-U-88 12 012 proposes bags of multilayer composite films for the inner pack, the composite films consisting of three layers of polymer film and one layer of metal foil to provide the adhesive/sealant with even better protection against the effect of moisture and/or air.
These known methods enable the transport containers to be more or less completely emptied so that they may be reused after removal of the empty inner pack and after reconditioning in the usual way, providing the containers are multi-trip containers. Non-reusable transport containers may be recycled as waste after removal of the empty inner pack.
In practice, however, it has been found that the prior art is in need of improvement in certain crucial aspects:
During the filling process, the pressure follower plate becomes soiled with material. During changing of the drum, this material is exposed to atmospheric moisture so that partial hardening occurs and, in subsequent filling cycles, leads to contamination of the material in the form of hard patches of skin or hardened lumps in the adhesive/sealant. PA1 The stiff cover plate according to DE-C-36 05 422 which, in practice, is generally a plate of polypropylene or polyethylene at least 2 mm thick remains in the empty inner pack together with the remains of the adhesive/sealant; it cannot be recycled at reasonable expense and thus adds considerably to the cost of the inner pack as a whole. In addition, it complicates recycling of the inner pack because, in practice, only multilayer composite films with a metal foil have been successfully used as the inner pack with the result that an inseparable mixture of different packaging materials is present. PA1 In practice, folding and welding the upper end of the inner pack has not been successful because unavoidable contamination of the wall material of the inner pack in the region to be welded with the material to be introduced (adhesive/sealant) or with auxiliaries, for example lubricants, does not offer any guarantee of a weld seam impermeable to air and moisture. Accordingly, the problem has hitherto been solved by tying the upper end of the inner pack together with several twisted wires. PA1 For emptying, a hole has to be cut into the surface of the inner pack, the adhesive/sealant being forced upwards through this hole by means of a pressure follower plate which compresses the inner pack. The inner pack in which the hole is cut often continues to tear, leading to unwanted soiling of the pressure follower plate at the emptying unit.